Recent evidence suggests that alterations in afferents or epithelial cells in the urinary bladder can lead to changes in neural excitability and may be part of the etiology of interstitial cystitis (IC). IC is a chronic clinical syndrome of unknown cause and presents with varying and complex sensory symptoms. This may involve a primary defect in afferent neurons or a change in their peripheral environment. Preliminary data indicate that IC in cats can alter the release of chemical mediators (nitric oxide, NO; ATP) from afferent nerves as well as the urothelium. It has been suggested that altered chemical release may influence afferent excitability as well as urothelial membrane function, by increasing the permeability to noxious substances. These data raise the possibility that the urothelium is involved in intercellular signaling in the urinary bladder and neural-epithelial interactions can modulate bladder function. The proposed experiments will use new methods such as cultured urothelial cells and a selective NO porphyrinic microsensor in a naturally occurring animal model of IC (feline interstitial cystitis), which has been demonstrated to have many similarities with IC in humans, to examine the hypothesis that chemical and/or intracellular signaling mechanisms in afferent or epithelial cells in the urinary bladder are altered in IC. Naturally occurring IC rather than acute bladder injury or inflammation models in healthy animals permit more relevant studies of pathophysiology of IC. Aim #1 will evaluation the characteristics of the urothelium in both normal and IC cats. The location of afferent nerves next to the urothelium suggests that urothelial cells might be targets for transmitters released from bladder nerves or that release by epithelial cells could alter the excitability of afferents. Aim #2 will evaluate the characteristics of bladder afferents in both normal and IC cats. We will evaluate the properties of normal bladder afferents to determine how afferents can be altered in IC. These studies may lead to selective pharmacologic interventions aimed at targeting neural-epithelial release or signaling defects and could provide a new prospective on the pathophysiology and clinical management of bladder disorders.